Unfortunately, the properties of an aluminum metallization layer which produce a film with desirable physical and electrical properties of resistivity uniformity of thickness grain size, etc. also produce a surface with a high specularity.
Highly specular surfaces in photolithographic processing produce unwanted reflections which can expose adjacent areas. Prior attempts to control such unwanted exposure of photoresist in adjacent geometries have included the application of antireflective coatings to the substrate surface before the depositing of photoresist. Such coatings have not generally been successful in reducing metal surface specularity to a desire extent. Another approach has been to use a dyed photoresist to absorb radiation reflected from the metal surface. The dyed photoresist, however, does not sufficiently reduce the level of unwanted reflections. A third approach has been to include an impurity atom such as oxygen in the film. Again, only limited success has been achieved using the latter technique.
It is, therefore, a principle object of the invention to provide an improved method of reducing the specularity of highly specular surfaces in the photolithographic processing of VLSI devices. It is a further object to provide a method of producing an antireflective coating on a highly specular surface prior to the application of photoresist.